Free standing wood wall lateral design 3

[SleeplessEngineer]

Hi everyone,
So we have free standing wood wall adjacent to steel stair for fire separation requirement. (IMO, it would be better to just leave steel stair alone, rather than adding fire rated wood wall; but I digress.)
I have added details and notes stating the wall panel would behave like a cladding element and the stair manufacturer needed to design for the wind loads on the wall.
But the client doesn't like it and reviewer asked for calculation of stair stating it can't be delegated upon permit since it involves fire requirement as well. The client wants the wall to be a separate stand-alone element since they intend to just get prefab stair without any specific design.
Is there a different approach? I can't design it as wood shear wall because the perpendicular wind load can not be carried; steel moment frame within the wall wouldn't work either for the same reason.
I feel like there is some simple and obvious approach, I'm just missing it.

Thank you for reading my post! I appreciate your time.

 

[phamENG]

You need something to carry the out of plane load on the wall. At that height, good luck. You'd be better off making the wall masonry and designing it as a horizontal cantilever or, if you wanted to get fancy, a panel fixed on two sides (at the building and at the foundation).

You're justified in your concern, and wood cannot do what it cannot do. Either the stair needs to be designed to take it, or the wall needs to be built from a material that can do it on its own.

On alternative would be steel moment frames perpendicular to the wall that they thread the stair through, but if you're going through all that trouble why not just design the stair? If they want something simple it's an easy set of calculations.

 

[SleeplessEngineer]

Thanks phamEng.
BTW, I forgot to mention that it's 4 story wall and not to mention if it were to be separated from stair, no diaphragm until the roof at top.
So I am little doubtful if I can make even masonry wall work here... If I make all the exterior wall masonry, to create the fixity you suggested; guaranteed the client is not coming back to us ever.
You are right, designing stair ourselves makes more sense; but I doubt we take on something like that at the moment due to our schedule.

Thank you for reading my post! I appreciate your time.

 

[SlideRuleEra]

...it's 4 story and not to mention if it were to be separated from stair, no diaphragm until the roof at top.
I feel like there is some simple and obvious approach, I'm just missing it.

Will appear to cost plenty, but compared with other "tricks" needed to make "something else" work may be more cost-competitive than thought at first look.

 

[JoshPlumSE]

I've done essentially the same thing as SlideRuleEra for a free standing wall. But, that was only one story. I don't think it would work for 4 stories.

In fact, I can't think of a way to get around the idea that the wall needs to be incorporated into the stair system.

What about communicating with the stair manufacturer and letting them know the wind load reactions that you will be imparting on their structure at each landing? That sounds a lot easier (and cheaper for the client) than any other solution I've heard.

 

[SleeplessEngineer]

Thanks SlideRuleEra and JoshPlumSE for your responses!
I don't quite understand how piles are gonna help here, even for one level. I did specify wall footing for full extend if that was not clear. Or am I misinterpreting your comments?
I was going to push this to be designed as cladding element, just wanted to double check; thanks all for your confirmations, I'm going ahead that way.

Thank you for reading my post! I appreciate your time.

 

[SlideRuleEra]

I don't quite understand how piles are gonna help here, even for one level. I did specify wall footing for full extend if that was not clear. Or am I misinterpreting your comments?

You are not misinterpreting comments, you just must not be familiar with use of cantilever driven piling.

I agree that cladding on the stair tower is a much better solution.

However, if you have no choice but to use a free standing wall (the title of your thread), piling can work, and likely be cost effective... even for 4 stories. When you see what even just the footing needed to resist wind loading overturning for a 4 story free standing wall will cost... revisit cantilever piling.

 

[SleeplessEngineer]

Thanks for the clarification Slideruleera, I understood now what you mean, a cantilever pile.
This is the best alternative to scare them a bit, haha. I understand your point on being cost effective. But the clients here hire cheapest contractors to do these kind of small wood framed residential buildings; and these contractors would not take a project involving driven piles or any other complexity. And they always ask for alternatives, so I am covered with this option!!!

Thank you for reading my post! I appreciate your time.

 

[SlideRuleEra]

Sleepless - I like that; use the piling concept to "scare" the client.

No matter what kind of free standing wall would be used, hard to imagine "cheap" contractors working on it 40'+ above the ground... they probably would not know how and certainly could not do it safely.

 

[XR250]

This is a really stupid detail. If the client is being stubborn, walk away.

 

[SleeplessEngineer]

I just called out the wall as cladding and given wind loads for stair manufacturer to design; also provided couple of details for connection of wood wall with the steel beam.
I didn't discuss any other option with the client. I have seen similar type of detail (HP) used in fence wall (perhaps 6' tall); but for 40' height, I don't even want to check the embedment and bracing required.

 

[Mike Mike]

sleepless - I have transferred out of plane wind loads from my wood wall, as EOR, into the delegated design steel stair before. In the photo below, I had another wood wall on the other side, unlike your case. It sucks and you should avoid it at all costs, but it can be done if necessary. Be sure to detail your steel-to-wood connections to allow wood shrinkage.